One stone, two birds: Polyaniline film with the difunctional characteristic of fast-response multi-color electrochromic and excellent super-capacitive behaviors

Electrochromic energy storage (EES) of polyaniline (PANI) materials holds great potential for improving energy efficiency in sustainable development. However, improving and balancing the electrochromic property and capacitance performance of the PANI material remains a significant challenge. Here, the galvanostatic (GS) electropolymerization technique is proposed to prepare a PANI film with outstanding electrochromic and excellent energy-storage properties. The evolutions of the structure mechanism of PANI films are revealed during its two-step growth process. The PANI film displays multicolor transitions across transparent, yellow, green, blue, and purple under applied potentials. Compared to those reported in the PANI-EES literature, the research achieves a greater variety of color variations. Furthermore, a large optical contrast of 50 % at 630 nm and an extremely fast electrical response time of 0.1 s are observed. The PANI film also exhibits a remarkably high specific capacitance of 509 F g⁻¹ and maintains high contrast. The fabricated EES device provides preliminary validation that the PANI film can simultaneously achieve pseudocapacitive behavior and electrochromic behavior in one device. This work achieves PANI films with multi-functional characteristics for various emerging multicolor electronics, supercapacitors, and EES optoelectronic devices.